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Differential vent tubes?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Suffergauge, Oct 17, 2002.

  1. Suffergauge

    Suffergauge 1/2 ton status

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    I have noticed the both my diffs have what look like vent tubes on them, where a hose should attach. There is also one on the t-case. What are these? How important are they to have hooked up?

    Thanks,
     
  2. heavy4x4

    heavy4x4 1/2 ton status

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    Yes, those are vent tubes. Yes, they should have hoses attached to them.
    On another post I think the decisive vote is 3/8" gas hose goes over the fitting and is clamped down (for the diffs anyway). Then, the hose is run as far up in the vehicle as possible (engine compartment/top of gas tank) so if/when you go offroad, water can not get in. It's also a good idea to have a hose so that moisture in the air doesn't condense inside your diff. Water and gear oil is not a good combination.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    On the '81 ups, the rear axle vent tube was run to the bottom of the bed, and had one of those little plastic caps on it.
    The front axle vent tube ran up to the frame, then to the drivers side of the core support, and was bolted in place there.

    I believe GM used those spring clips to retain them on the axle housings, like the one for the overflow bottle hose.
     
  4. k5geezer

    k5geezer Registered Member

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    It's very important to keep a tube on those vents. When the gear set gets hot, the air inside expands and vents out through the tube. If you cross deep water, the diff or trans gets cooled , the air inside cools, and air (or water) is sucked in through the vent. Keep the end of the vent hose higher than the deepest water you will cross. I think it is a good idea to put a filter on the end of the hose, similar to the ones used on the power brake vent. Helps keep things clean inside.
     
  5. Suffergauge

    Suffergauge 1/2 ton status

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    Right on, I will fix those today. What about the tube on the back of the t-case? There is one there but it is only like 4-5 in. long and had a bolt shoved in the end of it.
     
  6. imiceman44

    imiceman44 1 ton status

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    Same thing, anything that has oil in it and get's heat will need a vent, and any vent will need to be protected from water.
    I have always used a cheap gas fuel filterat the end, to protect it from water and keep it open, usually curving the hose down with the filter at it's end.
     
  7. wrathORC

    wrathORC 1/2 ton status

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    Doesn't the one on an automatic transmission only release fluid though? I'm not sure, the last time I had one apart it looked like that's the only time it's used. I bought some vacuum line to put on it but I haven't done it yet.

    Fish air stones work mighty nice for filters by the way. It's just like you can use the little one way check valve you use for fish air bubblers on your windshield wiper squirter lines to keep it from draining back in to the reservoir.
     
  8. trailblazer87

    trailblazer87 1/2 ton status

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    You need to extend any and all vents above the deepest water you will go through. If you think water and diff. lube are a bad combo. then your in for some fun when water gets in your tranny /forums/images/graemlins/eek.gif Instant clutch pack fry /forums/images/graemlins/blush.gif
     
  9. Suffergauge

    Suffergauge 1/2 ton status

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    Thanks everyone
     
  10. wrathORC

    wrathORC 1/2 ton status

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    Ah, yes, but isn't the one on the top of the transmission (with the short little metal tube) supposed to vent pressure only?
     
  11. imiceman44

    imiceman44 1 ton status

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    Still it could inhale water.
    Put tubes on everything, believe me you won't regret it
    /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
     
  12. wrathORC

    wrathORC 1/2 ton status

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    Did you bother to read my solitary sentence?

    If I said "vent pressure only" then how on earth is it going to suck water in? From what I've learned it only releases pressure if it gets too great. In other words it doesn't suck are in through the vent. Is this true? Speculation isn't worth anything. It doesn't make a whole lot of sense to run a tube from it 7 feet to under the hood if the only thing that's ever going to be in it is ATF.

    Someday when it quits raining and snowing I'll crawl under there and hook on a plastic bag and see if it sucks air in or not.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Ahh, speculation /forums/images/graemlins/smile.gif

    Yes, that tube will vent fluid if the tranny overheats. It will vent if the tranny is overfull. It can vent from other internal tranny problems.

    Whether there is some internal checkball or something for it, I don't know for certain. Just looked at the ATSG manual for the 200-4R (should be same for vent as most other GM trannies) and it doesn't mention the vent at ALL, except in diagnosis, and all it talks about is what can be wrong if fluid is coming out.

    Since they don't cover anything about "rebuilding" or working on the vent, I'd have to say that it is nothing more than a fitting on the top of the tranny, which vents the "crankcase", (tranny case in this instance) and therefore, if the tranny was submerged in cold water, you'd have the same problem as an axle, water could be sucked in. It's not venting tranny line pressure, its actually venting the inside of the case...so with the engine off, you should be able to overfill the tranny to the point that fluid starts spilling out of the vent.

    Since the internals should not be creating pressure (unlike an engine) more then likely once its warmed up, airflow in and out is not great.

    The only way I can see the "sucking water in" problem prevented would be a checkball in that location, which there is no reference to.
     
  14. CooknwithGas

    CooknwithGas 1/2 ton status

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    Why does the simple subject of vent tubes make people so "testy?" If you want a good laugh, read the thread in "The Garage" titled "Thanx." It started with another post about vent tube diameter, etc. I almost hurt myself laughing so hard the other night reading it.
     
  15. imiceman44

    imiceman44 1 ton status

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    Yes I did read the post and I thought I was clear.
    I have rebuilt many auto trannies, and I know for a fact that it's just a fitting, and if you want to make sure you don't get water in, you should extend it.
    About getting testy, I am never that emotionnal, I give my advise, if it's taken fine, if not fine.
    No body is perfect and whoever thinks he is, is his own problem.
    I don't think anyone on this forum knows everything and is just volunteering his time to help others, I have been into cars knee deep for more than 26 years and I still learn new things sometimes from newbies. They sometimes ask stupid questions that make you think harder and I value that, and no there are no stupid questions.
    Anyway there is no piece of the running gear that has a check valve for releasing pressure, because when the pressure is off it's going to need to suck in something back, either air, or if available water.
    And as usual, it's always better to be safe than sorry.
    /forums/images/graemlins/thumb.gif
    I will go check that thread now for a few laughs then. /forums/images/graemlins/rotfl.gif
     
  16. jjlaughner

    jjlaughner 3/4 ton status

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    Do you need to sealup the where the dipstick tube attaches to the tranny? If so how? Thanks, Jeremiah
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    If the seal there is good, no you don't. Had a TH400 in a car once that kept turning the tranny fluid pink. (water) I finally got fed up enough to pull the dipstick tube, to find that the seal was the incorrect one, and replacing that cured the water in tranny problem. So I'd say no, that won't leak as long as the seal is good.

    Of course, if you plugged the vent line then submerged the tranny, it *might* suck it in through there. Of course, it could suck it in through any gasket surface too.
     
  18. m j

    m j 1/2 ton status

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    Fram used to sell a clear plastic fuel filter that is perfect for a vent filter
    G-3 or G-4 is the p# depending on what size the line is(one is 5/16 one is 3/8 IIRC).
    I run them so I can see whether they have sucked anything up.
    they are better then the translucent or opaque ones commonly available
     
  19. TONYP

    TONYP 1/2 ton status

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    you can go to the chevy dealer and get the hose ends made of plastic, I went and was telling the guy what I needed and he looked at me like I was /forums/images/graemlins/crazy.gif, then another guy heard what I was looking for and spit out a part # and hooked me up...

    /forums/images/graemlins/angryfire.gif <font color="red"> ANGELS IN 6 </font color> /forums/images/graemlins/angryfire.gif
     

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